Devices having rotating members generally require balancing in order to keep vibrations that are caused by the rotating mass below a desired level. In a rotating-disc data storage device, for example, the disc (or disc stack) typically is precision balanced. Otherwise, vibrations associated with an unbalanced condition can impair the operable data transfer relationship between the read/write head and the rotating disc.
An offsetting mass is attached to the disc stack in order to balance it. Typically, the discs are attached to the hub of a spindle motor by a clamp ring. The clamp ring itself can be fashioned to provide the offsetting mass. The amount of offsetting mass is determined by the magnitude of the imbalance condition, and the rotational orientation of the offsetting mass is determined by the phase angle of the imbalance condition. There are a number of traditional approaches used to determine the magnitude and phase angle of the imbalance condition.
In data storage device manufacturing today, one such approach utilizes a motion-sensitive transducer, such as a piezoelectric transducer, to determine the translational movement imparted to the data storage device housing by the spinning disc stack. In some solutions the analog signal from the transducer is analyzed in the time domain to determine the vibration magnitude and phase. In some solutions the analog signal is translated to a digital pulse stream to facilitate analysis in the time domain.
In any event, a problem with these traditional approaches is that they are relatively too slow to keep pace with the station cycle time of high speed manufacturing processes, which in the data storage industry can typically be about four seconds or less. A reason for the slow response is because the vibration measurements must be taken at steady-state conditions. That is, the data collection activity cannot begin until the motor has accelerated the disc stack to operational speed, and until all transient surges associated with the acceleration have dissipated.
Another problem associated with traditional approaches is that they require extensive isolation from external vibration sources. This makes it virtually impossible to perform other manufacturing operations while the data collection activity is taking place. Attaching a fastener, for example, can create vibrations that could contaminate the measurements. For this reason it is not unusual to see manufacturing lines designed with dedicated vibration testing stations.
It has been determined that by detecting the actual speed of the disc stack and using the speed to trigger data collection activity, transient data can be analyzed during the disc stack acceleration. Furthermore, by translating the analog signal from the transducer to a digital signal in the frequency domain, the vibration analysis can be focused on the frequency associated with the rotational speed of the disc stack. This prevents vibrations not associated with the rotating disc from being included in the data collection activities. These enhancements lend greater speed and accuracy to the manufacturing process, and allow performing simultaneous operations on the data storage device during vibration testing. It is to these improvements and others as exemplified by the description and appended claims that embodiments of the present invention are directed.